Many of the power-type semiconductor devices (power modules) each have a structure in which a semiconductor element (hereinafter, referred to as “semiconductor chip” or simply “chip”) and an insulating substrate, or the insulating substrate and a heat-radiative metal plate are bonded together with solder or the like.
So far, lead (Pb)-containing solder has been used as a connection member for a semiconductor device required to have high heat resistance, in particular for the semiconductor device used for fields of an automobile, a construction machine, a railroad, an information device, and the like. However, an apparatus using a lead-free connection member is also widely utilized for reducing an environmental load.
In recent years, prompted is development of a wide gap semiconductor that uses SiC and GaN and the like to be capable of operating with high temperature and reducing size and weight of the apparatus. Incidentally, whereas an upper limit of operation temperature of a silicon (Si) semiconductor element is 150 to 175° C. in general, a SiC semiconductor element can be used at 175° C. or higher. However, when working temperature is high, heat resistance of 175° C. or higher is required also for various members used in the semiconductor device (power module).
In addition, in order to reduce cost, a demand for high efficient and stable bonding processes is increasing. In the SiC power module, particularly, since the cost of the SiC element is higher than that of the Si element, a high robust process and a mounting structure for achieving the same are demanded.
Incidentally, Patent Document 1 (Japanese Patent Application Laid-open No. 2005-116602) discloses a structure that improves a discharge characteristic in a circuit board used at a high voltage and is used for the power module and the like.